1. Field of the Invention
The present invention relates to a method of determining exposures, and more particularly to a method of determining exposures when a color printer having different functions and lightsensitive materials having different characteristics are used in conjunction.
2. Description of the Related Art
In a white-color subtractive color printer, light which has been transmitted through a negative film from a light source is measured by using photometers for blue (B), green (G), and red (R), and cut-filters (i.e. color compensating filters) of yellow (Y), magenta (M), cyan (C) are inserted into an optical path in response to output signals from the photometers, thereby automatically controlling the respective exposures of B-, G-, and R-sensitive layers of color paper. This type of color printer is provided with a correcting function for manually correcting exposures in automatic exposure control. The manual correction of exposures is effected by operating four keys, a D key for correcting the density of the overall picture, a Y key for correcting the density of Y, an M key for correcting the density of M, and a C key for correcting the density of C. In a correcting section of a printer, actual exposure E.sub.R, E.sub.G, E.sub.B are calculated in accordance with the following Formula (1): ##EQU1## where E.sub.RO, E.sub.GO, and E.sub.BO represent exposures of the three colors calculated by an automatic exposure control function on the basis of information on the negative (e.g., cumulative transmission density) measured by the photometers; I.sub.C, I.sub.M, and I.sub.Y represent amounts of variation per stage of the C key, M key, and Y key (color keys); I.sub.DC, I.sub.DM, and I.sub.DY represent amounts of variation per stage of the D key; and K.sub.C, K.sub.M, K.sub.Y, and K.sub.D represent values of the respective keys.
As can be understood from the above Formula (1), correcting calculations based o the operation of the C, M, and Y keys are respectively independent of the exposures of the three colors, and the operation of the key of any particular color exerts n influence on the exposures of the other colors. Accordingly, the variations of density of the printer in a case where the Y density is varied by operating only the Y key using a conditions-setting negative (a so-called Bull's eye or the like) in the above-described printer should become like those shown in FIG. 1. The abscissa of FIG. 1 represents a value (the number of stages) of the key , N denotes 0 (no correction), and A, B, C, and D denote -1, -2, -3, and -4, respectively. If the value of the key is altered by one stage, the exposure changes by an amount set in a 10-20% range.
However, spectral characteristics of the aforementioned cut-filters for exposures are considerably different from ideal spectral characteristics, so that one of the B, G, and R color components cannot be completely cut by a relevant cut-filter and, at the same time, the other color components are also cut by the same cut-filter by a considerable degree. In other words, these cut-filters constitute an exposure system in which a color mixture is present. In addition, although the boundaries of spectral sensitivity between the G-sensitive layer and R-sensitive layer of color paper are completely separated, the spectral sensitivity of the B-sensitive layer and that of the G-sensitive layer slightly overlap with each other (i.e., a color mixture takes place) in the vicinity of 550 nm. Furthermore, in the spectral characteristics of a color film, an overlapping is observed between the color-sensitive layers. Meanwhile, color separation filters for B, G, and R of an exposure system used in an integrating additive exposure type color printer provide characteristics close to theoretical values, so that these color separation filters make it possible to arrange an exposure system in which a color mixture is practically nil. Thus, since the spectral characteristics of cut-filters or color separation filters, the spectral sensitivity and color density of color paper, and the spectral density of a negative are not uniform, when the value of the Y key is varied as described above, the densities of M and C of a print also actually change, as shown in FIG. 2. Accordingly, as a result of operating the Y key, the operator is accustomed to the fact that the densities of M, Y, and C vary as shown in FIG. 2. This also holds true for the operation of the M and C keys.
In recent years, in order to improve the hues of color paper, attempts have been made to decrease the mixing of colors and improve processing by making improvements on lightsensitive materials and the exposure systems of printers. Thanks to these improvements, the variation of density of each color by the operation of the Y key becomes like the one shown in FIG. 3, and the degree of influence exerted on the other colors is reduced. However, in a case where an improved color printer and a conventional color printer are used in conjunction, there is a problem in that since the operator is not accustomed to the operation of the improved color printer, he or she frequently operates the improved color printer with the same feeling as that with which he or she operates the conventional color printer, so that prints whose hues are utterly different from the estimated hues are produced in large numbers. In addition, there is an additional problem in that since the conventional color printer and the improved color printer are operated with the same feeling, the hues of prints produced by these color printers differ from each other or vary. Furthermore, in order to solve these problems, it is necessary to deliberately make the operation of the conventional color printer different from the operation of the improved color printer, giving rise to the problem of deteriorated operating efficiency. These problems similarly occur when improvements are made on the lightsensitive materials without improving the color printer.